Thriving in the deep – These healthy deep reefs are located directly under shallow reefs degraded by storms and other stresses including coral bleaching and invasive crown-of-thorns starfish plagues. The deep coral is often flat because of the lack of light at depth.

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Photos:Australia's unexplored deep reefs

Roving submersibles – Remote operated vehicles (ROVs) were used to get to depths of around 100 meters, much deeper than normal scuba divers are able to go.

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Photos:Australia's unexplored deep reefs

Coral survey – "At the moment we know little about the extent of larval movements between the shallow and deep reef, but we are seeing species that exist in both zones," said Pim Bongaerts.

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Photos:Australia's unexplored deep reefs

Shallow reef damage – The image shows damage inflicted on Beaver Reef, part of the Great Barrier Reef, by the crown-of-thorns starfish, a species native to Australia which feeds on coral.

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Story highlights

Corals in deep water of Great Barrier Reef found to be thriving

Shallow reefs have been in serious decline in last 30 years

Deep-water survey has been exploring previously unstudied reefs

Deep corals could help those in shallower waters recover

A recent survey of the Coral Sea and Great Barrier Reef has found coral flourishing in deep waters, a stark contrast to the shallower reefs that have seen a drastic decline over the last few decades.

The healthy coral populations were discovered to be below 30 meters -- beyond the usual reach of most scuba divers -- and even found at depths of 80 meters, according to the Catlin Seaview Survey.

"The Holmes and Flinders Reefs in the Coral Sea are renowned for having been badly damaged, said Pim Bongaerts, of the University of Queensland's Global Change Institute, who was leading the deep reef survey.

"Yet we have found their deep reef zone is hardly disturbed at all. In fact the most striking thing is the abundance of coral on the deep reef. What has blown me away is to see that even 70 to 80 meters down, there are significant coral populations."

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Researchers say most of the damage to the shallower coral was wrought in recent years by a succession of powerful cyclones. Other threats that are hindering its ability to recover include the crown-of-thorns starfish, or COTS, a native species which feeds on coral, and coral bleaching that occurs when water becomes too warm.

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The deep reef survey team used remote operated vehicles able to reach depths of 100 meters, giving scientists a new view of hitherto unexplored reefs.

"It is surprising in this day and age, that below some of the most well-known reefs, which are so popular with divers, there is an almost entirely unexplored world and as a result an enormous amount of science to be done," said Bongaerts.

So far the team has completed four of its ten planned surveys at areas along the length of the 2,300 kilometer-long reef system and outlying atolls.

Bongaerts believes that the deep-water reefs might be able to help the shallower ones recover, as they have been seen to live in both depths of water.

"At the moment we know little about the extent of larval movements between the shallow and deep reef, but we are seeing species that exist in both zones," he said.

"There are clear differences we're observing. Corals are much flatter, more plate-like than the branching and domed shapes seen nearer the surface. This is the corals responding to the reduced light conditions and spreading out to maximize their exposure to light. So far below the surface, the light is blue because all other parts of the spectrum have been filtered out. It is a monochrome world until you turn on strong lights to reveal amazing, beautiful, fantastic colors."